Liquid jet recorder

ABSTRACT

A liquid jet recording system in which an electrically conductive tracing fluid is pressure ejected through a capillary nozzle to form a jet directed toward a recording sheet. A hollow control electrode is disposed around the point of drop formation so that a large potential pulse imposed between the fluid and electrode will cause the jet to break up, thus permitting the jet to be intensity modulated. The jet nozzle is supported in an element which can be moved to vary the direction of the jet axis periodically. In one system, a group of such nozzles, mounted to provide a corresponding group of jets in a common plane, can be moved periodically together.

United States Patent 1191 Hertz 14 1 June 5,1973

[54] LIQUID JET RECORDER OTHER PUBLICATIONS [76] Inventor: Carl Hellm hHe S O an Hertz et al., A Method for the Intensity Modulation of svagen8, 223 67 Lund, Sweden a Recording Ink Jet and Its Applications, ActaUniver- [22] Filed: Man 26, 1971 s1tat1s Lundensia, No. 15, 1967, 16pgs.

[21] Appl. No; 128,278 Primary EJ;aminer- Josep h W. HartaryAttorney-Robert J. Schiller and Nicholas A, [30] Foreign ApplicationPriority Data Pandlsclo Apr. 4, 1970 Sweden ..4528/70 [57] ABSTRACT l..P 20 4 6l Sept 97 Germany 7 l A liquid jet recording system in whichan electrically 521 US. Cl ..346/75, 346/140 "Ming fluid is i .ejected8" a [51] Int Cl G01 d /18 caplllary nozzle to form a et dlrected towarda [58] Fieid ll 75 140 recording sheet. A hollow control electrode isdisposed around the point of drop formation so that a large potentialpulse imposed between the fluid and [56] Referencgs cued electrode willcause the jet to break up, thus per- UNITED STATES PATENTS mitt ing thejet to be intensity modulated. The jet nozzle 1s supported in an elementwhich can be moved to Johnson fit al vary the direction of the jet axisperidica"y In one lg; gtonet system, a group of such nozzles, mounted toprovide a wee e 1 3,416,153 l2/1968 Hertz et a1. ..346/75 gg g zsgg g iggfi 12 3;; a common plane can 3,564,120 2/1971 Taylor ..346/75 x P v yg I 10 Claims, 10 Drawing Figures 3b 5 3c 5 3d 5 3e [0 1H lc ld- 7e 7 iU l] El 76 74 PAIENIEH N film 3.737. 914

SHEET 2 OF 3 PULSE GENERATOR PULSE I GENERATOR FIG. 5.

PULSE GENERATOR I SUPPLY Pulse ;;5 Car/ He/Mwfh Herfz 20V" PUMP iiii//Vl /V70/?.

ZI ATTORNEYS.

LIQUID JET RECORDER This invention relates to graphic recording systemand more particularly to a liquid jet recorder.

German Auslegeschrift DAS 1,271,754 US Pat. No. 3,416,153 describes amethod of intensity-modulating a tracing liquid jet and how this methodis practiced. In that method, use is made as tracing element of a fineliquid jet which is formed by ink ejected under high pressure from anozzle. Some millimetres in front of the nozzle, the jet spontaneouslybreaks up into droplets which are supplied to a record carrier followingexactly along a line. If an electrode is disposed in the vicinity ofthis point of drop formation and a sufficiently high electrical voltageis applied between said electrode and the tracing liquid, it is observedthat the liquid jet a short distance behind the point of drop formationdissolves into a diffuse cloud of droplets which produces only a verydiffuse coloration of the record carrier. This coloration may finally beeliminated altogether by suitable means so that one obtains on therecord carrier an ink trace which permits high-frequency electricmodulation.

An essentially simplified electrode system which exploits the samephysical phenomenon for modulating a liquid jet is disclosed in GermanOffenlegungsschrift 1,950,430 my copending U.S. application Ser. No.861,743 filed Sept. 29, 1969 which, inter alia, also treats of printingof alpha-numerical characters. However, the system defined therein forprinting such characters is relatively complicated and slow inmechanical respect, or requires a large number of liquid jets. Since thealphanumerical characters printed with such a system moreover permitonly with difficulty a better character resolving power than a X 7matrix, it is not possible by such system to print characters ofsufficiently high quality as may be required, for instance in typographyand other graphic printing methods. Similar difficulties are met with inthe use of the apparatus described in U. S. Pat. No. 3,298,030, which isbased on a quite different physical principle for controlling the inkdroplets, and therefore has to operate with considerably larger dropsthan does the present invention.

In contrast thereto, the present invention makes it possible to printalphanumerical characters of desirable quality with the aid of a simpleapparatus. Moreover, the invention opens up avenues for arranging alarge number of ink jets which can be electrically modulatedindependently of each other according to the abovementioned principle,in substantially closer relation than that attainable in using theprior-art electrode systems.

The above and further features of the invention will become apparentfrom the following, reference being made to the accompanying drawings inwhich:

FIG. 1 shows the principle of a liquid jet recording system in apossible embodiment of the invention;

FIG. 2 shows two examples of characters printed by this system;

FIG. 3 shows a recorder having a plurality of recording systems asillustrated in FIG. 1;

FIG. 4 shows two superimposed recorders of the type illustrated in FIG.3;

FIG. 5 shows a structural improvement of the recorder in FIG. 3;

FIG. 6 shows a recorder having considerably simplifled controlelectrodes;

FIGS. 7 9 show alternative embodiments of the control electrode in therecorder shown in FIG. 6;

FIG. 10 shows a device that prevents the tracing liquid from drying inthe nozzles.

An embodiment of the recording system which is the basis of theinvention is illustrated in FIG. 1. Fine capillary tube 12 is fixedlymounted in holder 5 and extends through a hole in plate 6 towardscontrol electrode 3. Plate 6 is secured to resilient means such as leafspring 7, the other end of which is attached to a support or holder 10.Electromagnet 8, through which flows alternating current from a-c source9, is attached to leaf spring 7 tocause the latter to oscillate so thatplate 6 swings in the direction of the arrow. Thus, the nozzle 4 at theend of the capillary tube 12 will be caused to swing back and forth in aplane at right angles to the direction of motion of the record carrier2. Means, not shown, are provided for supporting and moving recordcarrier 2, typically a paper strip. If s suitable tracing liquid is nowforced under high pressure through capillary tube 12, a fine linearliquid jet 1 will emerge from nozzle 4, and in the same manner ascapillary tube 12, the liquid jet will also swing back and forth andprovide an approximately sine-shaped recording trace 18 on the movingrecord carrier 2.

While travelling from nozzle 4 to record carrier 2, liquid jet 1 passesthrough control electrode 3 which is not shown in detail here becauseits construction is already described in German Offenlegungsschrift1,950,430. In order not to impede the oscillations of the liquid jet,the control electrode may be given, for instance, a rectangular crosssection. By means of control electrode 3, the shape of the liquid jetmay be influenced in a known manner by application of a control voltagederived from electronic generator 11. The latter applies a potentialbetween control electrode 3 and the tracing liquid in capillary tube 12.Because the liquid jet breaks up upon application of the potential asdescribed in German Auslegeschrift'DAS 1,271,754, in this manner thereis provided intensity modulation of recording trace 18. By suitableselection of the time sequence of the voltage pulses produced by thegenerator 1 1, optional alphanumerical or other characters can beprinted in this manner on the record carrier 2. An example is shown inFIG. 2 where the digit seven is reproduced in two different ways by thismethod, the broken line showing the path that the jet would be followingif the droplets were not then being dispersed. The broader areas showwhere, the potential having been removed, the droplets have made arecord.

An improvement of the quality of the characters printed in this way canbe attained by controlling the drop formation process in the mannerdescribed in the above-mentioned German Ofi'enlegungsschrift 1,950,430by means of, for instance, mechanical highfrequency oscillations at thenozzle 4.

Capillary tube 12 in the apparatus illustrated in FIG. 1 is, forinstance, a glass tube about 20 mm long and 0.1

mm thick, which at end 4 tapers into a nozzle of about 0.01 mm innerdiameter. The tracing liquid is forced through capillary glass tube 12under a pressure of 20 to 30 atm. gauge and forms a fine linearlycollected liquid jet. Plate 6 causes capillary glass tube 12 tooscillate typically at a frequency of about 200 to 1,000 Hz. The recordcarrier travels past capillary tube 12 at a constant speed of 20 to cmper second and is spaced approximately 25 mm from the nozzle 4.

The apparatus shown in FIG. 1, which causes the liquid jet mechanicallyto oscillate transversely, can also be realized in other ways. Forinstance, the liquid jet could also be translated in a periodicallyoscillating movement. Further, the desired periodical change indirection of the liquid jet could also be attained in another way, forinstance by suitable application of an electrical alternating fieldperpendicularly to the direction of the liquid jet 1. Alternatively,this can be realized with the aid of an alternating air stream directedperpendicularly at the liquid jet, or by supplying highfrequencymechanical oscillations at a frequency of 100 kHz and more to the end 4of the capillary glass tube 12.

It is advantageous for many purposes to arrange a plurality of therecording systems shown in FIG. 1 in juxtaposition. In that way, wholerows of alphanumerical characters can be traced simultaneously, as isthe case for instance in the printing registers of electronic computers.FIG. 3 shows a plan view of such an arrangement. I-Iere, five capillarytubes 12a thru 12e are arranged in juxtaposition so that their liquidjets la thru 1e are directed towards record carrier 2, which is movablein a plane normal to the common plane of the jets.

The liquid jets can be intensity-modulated individually by controlelectrodes 3a thru 32, each control electrode being connected to itsrespective electronic control circuit (not shown). All capillary tubes12a thru 12c are secured in holder '14 and each of them is passedthrough a hole in oscillating beam 13. The latter is se- It maybedifficult to dispose the recording systems illustrated in FIG. 1sufficiently close to one another so that character columns will not betoo widelyspaced apart. This difficulty can be overcome by the followingsystem of which also two or more can be used concurof record carrier 2so as to permit simultaneous tracing cured to two leaf springs 7a and 7band is caused to oscillate by electromagnet 8 in the manner previouslydescribed: The other ends of the leaf springs are connected to fixedsupport blocks 10a and 10b.

In this manner all liquid jets can be caused to oscillate synchronouslywith the aid of the electromagnet 8, the oscillatory movementcorresponding to that described above with reference to FIG. 1. Thiswill produce five juxtaposed sine-shaped recording traces on the recordcarrier 2. With the aid of control electrodes 3a thru 3e, liquid jets 1athru 1e can be electrically influenced individually in a suitable way,which results in an intensity-modulation of the recording traces, asalready described. If a suitable sequence of electrical pulses isapplied to each of the control electrodes, five alphanumerical or othercharacters can thus be printed simultaneously and independently of eachother on record carrier 2. Obviously, it is possible to trace in thisway any desired number of character columns beside one another if acorresponding number of the recording systems shown in FIG. 1 isarranged in juxtaposition.

.To ensure that the pulse sequences delivered by the electronic voltagegenerator to the various control electrodes are in correct time relationto the oscillation phase of the liquid jets, slot 15 is preferablyformed in beam 13. This slot partially shields a photoelectric sensorsuch as photodiode 17 from lamp 16. Upon oscillation of beam 13 bymagnet 8, an electrical alternating signal will thus be obtained fromthe photodiode, and the phase of that alternating voltage is thensynchronously associated with the phase of oscillation of beam 13. Suchan alternating voltage can also be obtained in a known manner with theaid of other transducers, such as piezoelectrical, capacitive, inductiveor resistive transducers in place of a photoelectric sensor.

or printing on both sides of the record carrier, since the jets heredescribed exert practically no force on the record carrier.

Furthermore, it is evident that the side walls of control electrodes 3athru 3e are not absolutely necessary for the function of the deviceshown in FIG. 3, provided that a correct geometry is chosen for thecontrol electrodes so as to insure that the electrical field at thepoint of drop formation of the individual liquid jets la thru 1e isdetermined only by the control electrode associated with the respectiveliquid jet. By this arrangement the recording systems can be arrangedmore closely together than what is possible with the recorderillustrated in FIG. 4.

FIG. 5 shows part of an exemplary construction of two juxtaposedrecording systems in such an arrange ment. With a distance of 4' mmseparating the control electrodes, the spacing'between each of the uppercontrol electrode portions such as plates 3f and the corresponding lowercontrol electrode portions such as plate 3g should typically amount toabout 1 mm. The upper.

and lower portion or plates of each control electrode pair such as 3fand 3g, or 3h and Bi are conductively interconnected and coupled to arespective electronic voltage pulse generator such as 11f and 11):. In aknown manner at least the surface of thecontrol electrodes facing theliquid jet are electrically conductive and porous, and are connected toa suction means not shown in FIG. 5) for sucking away any 'of thetracing liquid striking such'porous surfaces. Alternatively, also eachof the control electrode portions may be individually connected to acontrol pulse. generator, which implies a more complex control with twoindependent signals per jet, one for each electrode plate or portion.

In the recorder shown in FIG. 5 all control electrode pairs have to beinsulated from each other. With a large number of juxtaposed jets, thisimplies because of the suction means (not shownin FIG. 5) .practicaldifficul'ties such that it is impossible to build a recorder accordingto FIG. 5 if the liquid jets have to be spaced less than some minimumdistances apart. Therefore, alternatively, as shown in FIG. 6, a single.control electrode 3j composed for instance, of two parallel plates canbe substituted for the system of control electrodes of FIG. 5. When thecontrol voltages producedby electronic voltage pulse generators shown as11k and 11m are applied with the-aid of respective electrodes 19k and19m to the tracing liquid in capillary tubes 12k and 12m, the liquidjets can be modulated also in this way, since according to GermanOffenlegungsschrift 1,950,430, the electrical control of the jet isdependent only upon the voltage difference between the liquidv jetemerging from the capillary tube and the control elec- 12k and 12m areagain secured like in FIG. 3 in holder 14 and are caused to oscillate bymotion of beam 13. To avoid pollution of the tracing liquid by productsof electrolysis, the electrodes 19k thru 19m may be enclosed withincorresponding filters.

It is clear that the control electrode 3j common to all liquid jets maybe connected to ground or to a constant voltage. Alternatively, however,the control electrode 3j can also be connected to an electronic voltagepulse generator 23, which makes it possible collectively to influenceall liquid jets. In this case, also, the control electrode 3j can becomposed of two porous electrically conductive and electricallyinterconnected plates which are about 20 mm wide and are disposed about0.5 mm above and beneath the plane defined by the plane of oscillationof the liquid jets. To such away scattered tracing liquid that isintercepted by the control electrode, the plates of the controlelectrode 3j may be provided with internal passageways connected tosuction pump 24. Alternatively, these plates may be provided with asuction sleeve as in German Offenlegungsschrift 1,950,430.

It is obvious that the arrangement shown in FIG. 6 may also be providedwith more than the two exemplary juxtaposed capillary tubes 12k and 12m.Also, control electrode 3j may be given other shapes, and, inparticular, the distance between the plates of the control electrode mayvary or be tapered in the direction of the jet. The two plates of thecontrol electrode 3j may be provided with different potentials. Finally,control electrode 3j may be formed in a unitary structure which for eachtracing jet has a tubular passage the axis of which coincides with theaxis of the jet. FIG. 7 shows such an embodiment wherein the passageshave rectangular cross sections. Moreover, a slot-shaped porous shuttermay be interposed between control electrode 3j and the record carrier 2,and this shutter in turn may have applied to it a suitable constantvoltage.

If capillary tubes 12 are arranged in vertical position, the recordershown in FIG. 6 can be still further simplifled. FIG. 8 shows anembodiment, chosen by way of example, of such a recorder in which thecontrol electrode consists of two metal sheets 3k and 3m. The tracingliquid which has deposited on the inner side of the control electrodeflows by gravity into grooves k and 25m and along said grooves to anoutlet at the lateral end of the electrode, whereby the suction pump 24shown in FIG. 6 can be dispensed with. By arranging also the recordershown in FIGS. 3-5 and 6 in vertical position, gravity can be exploitedto carry away the tracing liquid.

It is obvious that the arrangements shown in FIGS. 3 thru 8 inclusivepermit an intensity modulation of the recording traces also in the casewhen the liquid jets are not caused to oscillate but are stationary. Inthis latter case, it may be advantageous if the line in which recordcarrier 2 intersects the plane formed by the liquid jets does not lie atright angles to the direction of motion of the record carrier but almostcoincides with said direction. Furthermore, it is likewise not necessarythat the liquid jets pass through control electrode 3j in parallelrelation. It may rather be advantageous for certain uses if the jets aredirected substantially concentrically in a common plane towards apointin the vicinity of the record carrier 2, as is shown in plane view inFIG. 9.

As already described in German Offenlegungsschrift 1,950,430, the partof the tracing liquid intercepted by control electrode 3 is sucked awayand is thus lost. This can be prevented if, for instance, in FIG. 6, thetracing liquid sucked away by suction pump 24 is returned to the supplycontainer 20a. In order that the tracing liquid may not lose solvent,such as water, and gradually thickens, fresh solvent can be added incorrect amounts. This procedure may be automatized by run ning thetracing liquid through a semipermeable tube surrounded by a solution ofsuitable osmotic pressure. The correct solvent concentration will thusbe constantly adjusted in the tracing fluid by osmosis.

Mostly, relatively fine nozzles 4 are utilized at the ends of thecapillary tubes 12 in the arrangements shown in FIGS. 1 thru 5. Oneshould therefore retard or prevent, by selecting suitable tracingliquids, drying of the tracing liquid which would tend to clog nozzles 4at shutdowns. This risk can be eliminated by covering nozzles 4 atshutdowns with a suitable liquid, whereby drying of the tracing liquidis prevented. To this end, oscillating beam 13 may be designed forinstance as a hollow or double-walled structure (as shown in FIG. 10)into which capillary tubes 12 open through holes, as alreadyhereinbefore described. In front of nozzles 4 at' the ends of each ofcapillary tubes 12 there are arranged apertures 26, about 1 mm indiameter,'through which the liquid jets can pass unobstructedly. Iffollowing shutdown beam 13 is filled with a protective liquid throughflexible supply conduit 27 from closed supply container 28, theprotective liquid will cover nozzles 4. The liquid level in thecontainer should be so selected that the liquid certainly penetratesinto beam 13 but is prevented by surface tension from escaping throughapertures 26. If container 26 is also connected by appropriate valving(not shown) to suction pump 24 which, as shown in FIG. 6, is alsoutilized to suck away tracing liquid fron control electrode 3j, thenautomatically when the arrangement is made operative the liquid willimmediately be sucked out of hollow beam 13.

The arrangement illustrated in FIG. 10 has the further advantage thatthe front wall of beam 13 can serve to shield electrically nozzles 4from each other, it that front wall is made from conductive material andis connected to a suitable voltage. Alternatively, however, otherembodiments of beam 13 are conceivable. Thus, the double wall of thebeam at each position of the capillary tubes can be replaced by a smallvertical tube secured to beam 13 and so arranged as to convey protectiveliquid to each nozzle 4 of a respective capillary tube 12.

The tracing speed of the recorders illustrated in FIGS. 3 to 8 inclusivecan be in the order of 20 to I00 lines per second, and therefore it isnot necessary to associate with each character position a separateelectronic coding unit which produces the correct voltage pulsesequences for the tracing of the characters. If a shift register isassociated with each character position, it is in fact, possible tocarry out recording of all characters in a line during the time it takesthe paper advance mechanism to provide the necessary line spacing.During this time, for instance, digital information delivered in seriesform by an electronic computer can be recoded digit by digit in acentral coding unit and be stored in the shift registers in such a waythat a parallel relatively slow reading of all shift registerssimultaneously supplies to the control electrodes in each tracingposition precisely the pulse sequence that is necessary to trace thecharacter read into the respective shift register. It may be desirableto connect a voltage amplifier between the shift register and controlelectrode '3 or the electrodes such as 19k. It is obvious that readingof the information from the shift registers must take place in correcttime relation with the mechanical oscillations of beam 13. Suchsynchronization may be realized by means of the electrical signal fromphotodiode 17 or in another manner,

What is claimed is: l. A liquid jet recorder for writing with anelectrically conductive marking fluid on a receiving surface movablealong a first path, said recorder comprising ,in combination,

a plurality of capillary nozzles juxtaposed so that a correspondingplurality of jets of said fluid can be pressure ejected therefrom towardsaid receiving surface, said nozzles being at corresponding ends of alike plurality of capillary tubes mechanically coupled to one another,control electrodes disposed adjacent the point of drop formation of eachof said jets for applying a respective control voltage so as tointensity modulate each of said jets independently of one another,

means for periodically and simultaneously in tandem moving saidcapillary tubes with respect to said electrode means substantially alonga common path substantially transverse to both the path of motion ofsaid receiving surface and the axes of said jets.

2. A recorder as defined in claim 1, including transducer means forconverting the periodic movement of said tubes into alternatingelectrical synchronizing signals substantially throughout each period ofmovement.

3. A recorder as defined in claim 2 wherein said tubes are flexible andsaid means for moving is connected for applying bending forcestransverse to the longitudinal axesof said tubes.

4. A recorder as defined in claim 1 including a common control electrodefor at least one group of said 'ets. J 5. A recorder as defined in claim1 including individual sources of supply of said tracing fluid for eachof said jets, individual electrodes each associated with a correspondingone of said sources for imposing a potential on the fluid in saidsource.

6. A recorder as defined in claim 1 wherein all of the axes of said jetsare in approximately parallel relationship in a substantially commonplane.

7. A recorder as defined in claim 1 wherein all of the axes of said jetsare in approximately convergent relationship to a common point in asubstantially common plane.

8. A recorder as defined in claim 1 including means I for covering theopening in said nozzles with a protective liquid during a period whensaid fluid is not being ejected.

9. A recorder as defined in claim 8 including pump means for removingsaid liquid prior to ejection of said fluid from said nozzles.

10. In a liquid jet recorder for pressure ejecting toward a recordingsurface a plurality of jets of an electrically conductive tracing fluidfrom corresponding nozzles, and including means for periodically varyingthe direction of said jets along paths substantially normal to the jetaxes, electrical means for applying electrical potentials for each ofsaid jets, and means for supplying said fluid to said nozzles from acommon fluid source, the improvement wherein said means for supplyingcomprises a plurality of tubes each connecting a corresponding one ofsaid nozzles to said common source, each of said tubes being dimensionedin length and cross-section so that the electrical resistivity of saidfluid in each of said tubes is sufficiently high to constitute anelectrical buffer between said nozzles with respect to said potentials.

1. A liquid jet recorder for writing with an electrically conductivemarking fluid on a receiving surface movable along a first path, saidrecorder comprising in combination, a plurality of capillary nozzlesjuxtaposed so that a corresponding plurality of jets of said fluid canbe pressure ejected therefrom toward said receiving surface, saidnozzles being at corresponding ends of a like plurality of capillarytubes mechanically coupled to one another, control electrodes disposedadjacent the point of drop formation of each of said jets for applying arespective control voltage so as to intensity modulate each of said jetsindependently of one another, means for periodically and simultaneouslyin tandem moving said capillary tubes with respect to said electrodemeans substantially along a common path substantially transverse to boththe path of motion of said receiving surface and the axes of said jets.2. A recorder as defined in claim 1, including transducer means forconverting the periodic movement of said tubes into alternatingelectrical synchronizing signals substantially throughout each period ofmovement.
 3. A recorder as defined in claim 2 wherein said tubes areflexible and said means for moving is connected for applying bendingforces transverse to the longitudinal axes of said tubes.
 4. A recorderas defined in claim 1 including a common control electrode for at leastone group of said jets.
 5. A recorder as defined in claim 1 includingindividual sources of supply of said tracing fluid for each of saidjets, individual electrodes each associated with a corresponding one ofsaid sources for imposing a potential on the fluid in said source.
 6. Arecorder as defined in claim 1 wherein all of the axes of said jets arein approximately parallel relationship in a substantially common plane.7. A recorder as defined in claim 1 wherein all of the axes of said jetsare in approximately convergent relationship to a common point in asubstantially common plane.
 8. A recorder as defined in claim 1including means for covering the opening in said nozzles with aprotective liquid during a period when said fluid is not being ejected.9. A recorder as defined in claim 8 including pump means for removingsaid liquid prior to ejection of said fluid from said nozzles.
 10. In aliquid jet recorder for pressure ejecting toward a recording surface aplurality of jets of an electrically conductive tracing fluid fromcorresponding nozzles, and including means for periodically varying thedirection of said jets along paths substantially normal to the jet axes,electrical means for applying electrical potentials for each of saidjets, and means for supplying said fluid to said nozzles from a commonfluid source, the improvement wherein said means for supplying comprisesa plurality of tubes each connecting a corresponding one of said nozzlesto said common source, each of said tubes being dimensioned in lengthand cross-section so that the electrical resistivity of said fluid ineach of said tubes is sufficiently high to constitute an electricalbuffer between said nozzles with respect to said potentials.